The invention relates to an improved method and apparatus for metal container manufacture, and more specifically to apparatus and a method for providing a bead proximate the upper peripheral edge of a tin box.
Metal containers with lids are provided with a bead adjacent an upper edge of the container to enable the lid to frictionally engage therewith and/or to prevent a corresponding bead provided on the edge of a peripheral skirt of a lid from easily sliding off the outer surface of the container. The bead is required to be of the same dimensions around the entire upper edge of the container so that the lid has equal contact along the same. This ensures a good fit of the lid with the container and also makes the interior of the container as airtight as possible. This is particularly important when the container is being used to store food products or dried products where the ingress of air and moisture needs to be limited.
Metal containers are also provided with a, usually inwardly disposed, curl on the uppermost edge of the sidewalls. This provides the container with a neat and safe finish to the edge, which is both appealing to the eye and prevents a potentially sharp edge being exposed to a user of the container.
A conventional method of providing the bead and curl typically involves three steps. Firstly, an end-less tube having the cross-section of the completed container is placed on a mandrel and clamped such that the mandrel is internally disposed on the walls of the tube. The mandrel is comprised of a plurality of wedges which can slide relative to one another to effect the expansion of said mandrel, and on the external surface thereof there is provided a bead-like protrusion. Secondly, a forming tool also comprised of a plurality of inwardly disposed wedges capable of relative motion with respect to one another such that forming surfaces thereof can approach and retreat from the mandrel disposed internally of the container, hereinafter referred to as the inner mandrel. The surface of the forming tool is commonly provided with a bead-like groove into which the material of the container can be deformed by the action of the bead-like protrusion on the inner mandrel. The inward and outward actuation of the surfaces of said forming tool may be effected by angular displacement of a further component acting around the said forming tool.
In use, the inner mandrel is expanded outwardly against the side walls of the container with the forming tool being simultaneously actuated such that the surfaces thereof approach and are brought to bear against the outer surfaces of the side walls of the container. The bead-like protrusion on the surface of the inner mandrel is slightly displaced inwardly from the free edge of the tube and in the region where the bead-like protrusion contacts the side walls, the material is plastically deformed into the bead-like groove provided in the surface of the forming tool. Finally, a series of pins are raised which drive a ring component, having a groove cut therein of the same shape in plan as that of the cross-sectional shape of the container, upwardly such that an already partially formed curl known as a pre-curl on the uppermost edge of the sidewall of the tin box is received in said groove. The profile of the groove and the extent of the upward motion of the ring component are such that the pre-curl is further deformed within the groove to create a complete curl.
A disadvantage of the conventional method is that the various portions of the forming tool have to be accurately positioned to ensure equal clamping pressure of the tin box side wall between the mandrel during the formation of the bead-like protrusion therein.
This ensures that the bead is of the same general profile around the entire surface of the tin enabling a good fit with the lid. Any imbalance in the clamping force or imprecise alignment of the forming tool and mandrel can result in imperfect manufacture, in particular by imparting an undesirable outward flare of the side wall from one end to the other and along a portion or the whole of said side wall. The precision required is frequently either not achieved or is lost during regular use of the apparatus. In severe incidences of the problem, the dimensions of the lids for the containers are then required to be enlarged to allow for greater clearance and thus permit the depending annular skirt of the lid to pass completely over both the uppermost curled edge of the box and over the bead.
A further disadvantage is the number of components which are required to be independently actuated. Specifically, the mandrel disposed within the tin box is usually expanded immediately prior to the formation of the bead by the actuation of components which move axially parallel with the axis of the box, whereas the forming tool or tools are actuated by a rotationally moving component around the said forming tool and are required to be moved towards and away from said inner mandrel in a direction perpendicular to the axis of said box. This problem serves to increase the size and complexity of the apparatus.
It is therefore an object of the present invention is to provide a more efficient method and apparatus for manufacturing of a bead and curl on a metal container which overcomes the above mentioned problems.
It is a further object of the invention to provide an apparatus which provides both bead and curl by virtue of the driven linear actuation of a single component.
According to a first aspect of the present invention there is provided an apparatus for providing at least a bead on a side wall portion of a metal container, said apparatus comprising a mandrel over which said side wall portion is disposed, said mandrel having reaction members with reaction surfaces for supporting the side wall portion internally, the apparatus further comprising a plurality of forming members surrounding the mandrel having forming surfaces being substantially parallel with the reaction surfaces but separated therefrom to define a gap between said surfaces which receives the said side wall portion, said reaction members and forming members being capable of displacement towards and away from one another such that the gap between the reaction surfaces and the forming surfaces can effectively expand and contact, said reaction surfaces and said forming surfaces being provided with complementary formations thereon to deform the side wall portion therebetween and form a bead therein, characterized in that the reaction members and the forming members are moved back and forth by virtue of cam means particular to each reaction member and forming member, said cam means being provided on an actuating member having a linear reciprocal motion parallel with the axis of the mandrel.
Preferably the cam means comprise a plurality of pins or plates standing proud of one surface of the actuating member having inclined cam surfaces at their extremities on which cams rotationally mounted on the reaction and forming members can travel.
Preferably the inclination and disposition of the cam means which cause linear translation of the reaction members and those cam means which cause linear translation of the forming members can be different so that the translation of either reaction or forming members can be began before the other or at the same time, and also the velocity and/or acceleration of said members can be predeterminedly controlled.
Preferably the reaction members and the forming members are springingly biased against the cam means to ensure that as the actuating plate is moved axially away from the mandrel, the said reaction members and forming members automatically move away from one another. This feature also facilitates the loading and unloading of the side wall portion of a container into and from the machine.
It is to be mentioned however that the apparatus according to the invention may only provide a bead, and it is not essential to the invention that both bead and curl be created consecutively, although this is preferable.
It is most preferable that the actuating plate is further provided with or communicates with curl forming means disposed around the periphery of said side wall portion and underneath the same.
Preferably the motion of the actuating plate causes corresponding motion of the curl forming means relative to the peripheral edge of the side wall portion and in the same plane, and preferably this relative motion is achieved as the actuating plate approaches its maximum displacement from the mean about which it reciprocates.
Preferably the curl forming means and/or the actuating plate are provided with stop means to limit the relative motion of the side wall portion and said curl forming means and thereby limit the size of the finished curl.
Preferably the peripheral edge of the side wall portion is initially provided with a pre-curl prior to the insertion of said portion into the apparatus.
According to a second aspect of the present invention there is provided a method of manufacturing a bead and curl on a side wall portion of a metal container, said method comprising the steps of disposing said side wall portion around a mandrel, clamping said sidewalls of said container between reaction surfaces of reaction members provided on the mandrel and forming surfaces substantially parallel with the reaction surfaces and provided on forming members suitably arranged around the reaction surfaces to define a gap of the same general shape as the cross-sectional shape of the container, said reaction surfaces and said forming surfaces having complementary formations and being capable of being displaced towards and away from one another, forming a bead in said sidewall portion by compressing the said side wall portion between said reaction surfaces and said forming surfaces, and subsequently causing curl forming means to move relative to the side wall portion thereby forming a curl, characterised in that the displacement of the reaction members and forming members is laterally outwardly and inwardly of the mandrel whereas the relative motion between the curl forming means and the side wall portion of the container is axially of the mandrel, and both motions are caused by the motion of an actuating plate translating back and forth in the same general direction as the axis of the mandrel.
Preferably said actuating plate is slidably located on a spindle. In addition, the actuating plate can be spring biased on the spindle.
During a cycle of operation of the apparatus, the actuating plate rises up the spindle and thus the cam means, i.e. pins or plates also move vertically upwards. The inclined cam surfaces on said pins or plates cause lateral displacement of the reaction members and subsequently the forming members, whereafter continued upward motion of the actuating plate causes relative movement between the side wall portion and curl forming means. After the bead and curl have been completed, the actuating plate retracts, thus lowering the pins which in turn releases the formed curl from the curl forming means and subsequently the side wall portion from between the reaction and forming surfaces.
An advantage of the present invention is that the bead and curl operation is performed in a single vertical motion rather than three separate steps as in the prior art. The reduction in the number of steps of the process increases the efficiency of the same.